Method of making a fuel injector

ABSTRACT

AN ELECTROMAGNETIC FUEL INJECTOR FOR A FUEL INJECTION SYSTEM IS PROVIDED WITH A SOLENOID WINDING WHICH, WHEN FED WITH ELECTRICAL OPERATING CURRENT, PRODUCES A SATURATED MAGNETIC FIELD IN AT LEAST PART OF A MAGNETIC CIRCUIT, WHICH FIELD IS USED TO ATTRACT A MEMBER CONTROLLING THE VALVE MEANS OF THE INJECTOR AND HENCE THE FUEL FLOW. THE VALVE MEANS MAY INCLUDE A PLUNGER HAVING A TIP PORTION OF A PLASTICS OR RUBBER-LIKE MATERIAL TO ENGAGE THE VALVE SEAT. METHODS OF ATTACHING THE TIP PORTION TO THE PLUNGER ARE ALSO DESCRIBED.

United States Patent [191 Kent [ METHOD OF MAKING A FUEL INJECTOR [75]Inventor: Peter Michael Kent, Rugby, England [73] Assignee: BricoEngineering Limited,

Warwickshire, England 22 Filed: Dec. 15, 1972 21 Appl. No.: 315,430

Related US. Application Data [62] Division of Ser. No. 171,472, Aug. 13,1971, Pat. No.

[52] US. Cl. 29/l56.7 R, 29/157.1 R, 29/445, 29/446, 29/526, 251/357[51] Int. Cl B2lk l/20, B23p 13/00 [58] Field of Search... 29/445, 446,157.1 R, 156.7, 29/526; 239/412, 533, 585; 251/356, 357 X,

[56] References Cited UNITED STATES PATENTS 9/1932 French 239/585 X6/1964 Rotheraine et a1. 251/357 1 June 28, 1974 3,236,496 2/1966Rosenstein et a1 251/357 3,381,351 5/1968 Szwargrlski 251/358 X3,381,352 5/1968 Linder et a1. 29/156.7 R 3,608,171 9/1971 Stradtmannm"29/156.7 R

3,625,245 12/1971 Biermann 251/357 X 3,672,031 6/1972 Negrini 29/445 X3,685,135 8/1972 Letters 29/445 X Primary Examiner-Charlie T. MoonAttorney, Agent, or Firm-Brisebois & Kruger [5 7] ABSTRACT ing a tipportion of a plastics or rubber-like material to engage the valve seat.Methods of attaching the tip portion to the plunger are also described.

4 Claims, 3 Drawing Figures 1 METHOD OF MAKING A FUEL INJECTOR This is adivision, of application Ser. No. 171,472, filed Aug. 13, 1971, now US.Pat. No. 3,773,265.

This invention relates to fuel injectors, and particularly, but notexclusively, to fuel injectors for supplying fuel to an internalcombustion piston engine.

According to one aspect of the invention, in an electromagnetic fuelinjector a winding, when fed with electrical operating current, producesa saturated magnetic field in at least part of a magnetic circuit, themagnetic field being arranged to produce a force to move a membercontrolling the flow of fuel from the injector.

Preferably means are provided for optionally adjusting the forceproduced on the member by the magnetic field.

Conveniently the position of a ferromagnetic saturatable body isadjustable in an aperture in that portion of the magnetic circuit whichbecomes saturated in operation, whereby to adjust the magnetic fieldobtained when the portion of the magnetic circuit is saturated.

Suitably the magnetic circuit includes a central core which becomessaturated, the core having an axial bore extending into the saturatedportion, and a ferromagnetic rod axially adjustable along the bore.

According to another aspect of the invention, a fuel injector in whichpressurised fuel is periodically admitted to or cut off from an injectororifice by a valve means includes a seating face against which a plungeris urged to seal the pressurised fuel from the orifice and from whichseating face the plunger is withdrawn to admit the pressurised fuel tothe orifice, and in which the portion of the plunger which contacts theseating face is of a plastics or rubber-like material.

The plunger is generally of metal and has a tip portion fastened theretoof plastics or rubber-like material for making sealing contact with theseating face.

Suitably the seating face is of hollow conical form. Preferably the saidportion of the plunger which contacts the seating face is ofpart-spherical form.

Conveniently the metal portion of the plunger has an axial bore intowhich a stem on the plastics or rubberlike tip is fastened. Preferablythe stem is a press fit into the bore.

Desirably the stem is additionally fastened in the bore by a diametralpin-passing through the stem and the surrounding metal.

Advantageously the tip has a coaxial bore extending through the stem andto a point in the tip adjacent the portion which contacts the seatingface.

Preferably the plastics material is an acetal copolymer.

According to a further aspect of the invention, a method of making afuel injector of the kind having a plunger of which a metal portion hasa bore into which is fastened a stem of a tip of plastics or rubber-likematerial, said tip being for sealing against a seating face of the fuelinjector, includes inserting the stern into the bore, loading the tiptowards the metal portion with a load at which the tip material juststarts to plastic flow, and mechanically securing the stem to the metalportion while so loaded.

Suitably the method includes drilling a diametral bore through the stemand metal portion and inserting a fastening pin therein while the tip isstill loaded.

Conveniently the method includes subsequently removing the load on thetip, rough shaping the portion of the tip for contacting the seatingface, annealing the plunger at an annealing temperature for the plasticsor rubber-like material, cooling the plunger and finish shaping theportion of the tip.

Preferably the method includes raising the assembled injector with thetip subject to its normal working load against the seating face, to atemperature at which the plastics or rubber-like material just starts toplastic flow.

The invention is described, by way of example only, with reference tothe accompanying drawings in which:

FIG. I is a longitudinal section through a fuel injector,

FIG. 2 is a longitudinal section through a solenoid shown in part ofFIG. 1, and

FIG. 3 shows part of FIG. 1 to an enlarged scale.

In FIG. 1 a fuel injector has a tubular metal body 10 into-the lower endof which is pressed a metal thimble 11. A conical seating face 12 isformed inside the thimble 11 from which a central passage 13 leads to athin 'metal disc 14, held by peening into a depression in the end of thethimble 11. A very fine hole of carefully selected diameter serves as ametering spray orifice through the centre of the disc 14.

In use the fuel injector is located in an unshown injector housingpositioned so that fuel issuing from the spray orifice discharges intoan inlet duct of an internal combustion engine. The injector is locatedin two concentric bores in the injector housing and is sealed in thebores by two O-rings l5, 16. The junction between the injector housingbores forms a step against which a flexible flange l7 seals. The spacein the injector housing between the O-ring l5 and flexible flange 17forms a fuel inlet chamber to the injector, and the space between theflexible flange l7 and the O-ring 16 forms a fuel outlet chamber. Theflexible flange 17 forms an integral part of the nylon filter 18 havinga circumferential band of fine integral filter panels above and belowthe flexible flange 17 so that fuel is filtered before entering theinjector and again before leaving it.

The filtered fuel passes to the interior of the injector body 10 throughradial drillings 19. As described below, some fuel passes downwardly andout through the passage 13 and metering orifice in the disc 14. Surplusfuel rises to a chamber 20 and thence passes downwardly through passages21 and out through the filter 18, as shown by the arrows.

Passage of fuel through the orifice in the disc 14 is controlled by anaxially movable plunger having a tubular metal shaft 22 into the lowerend of which is fastened a hemispherical ended tip 23 of an acetalcopolymer, such as Delrin" or other suitable plastics or rubber-likematerial. The metal shaft 22 is guided by guide blocks 24, 25 fastenedin the injector body 10 and the thimble 11 respectively. A precompressedlow rate helical spring 26 acts between the guide block 24 and a collar27, held to the shaft 22 by a spring clip 28, to urge the tip 23 againstthe conical seating face 12 to cut off the supply of fuel to the passage13.

At the upper end of the shaft 22 is fastened a soft iron mushroom-shapedhead 29 having a top face 30 which is accurately normal to the axis ofthe shaft 22. This accuracy is achieved, without expensively accuratema- I chining of the shaft 22 and head 29, by providing a bore by theuse of an appropriate adhesive.

A solenoid unit 32 is held in a counterbore 33 against a shoulder 34' inthe injector body It), by a nut 35. The solenoid has electricalterminals 36, and when fed with electrical current, generates a magneticfield which attracts the head 29 and shaft 22 upwards to close a smallaccurately set gap between the face 30 of the head 29 and the loweropposing face of the solenoid 32. As long as the electrical currentflows the shaft 22 will hold the plastics tip 23 a fixed distance ofithe conical seating face 12 so that fuel will flow through the orificein the plate 14 at a constant rate, if the fuel pressure differenceacross the orifice is constant.

In order to achieve good sealing of the tip 23 to the seating face 12and reliable operation, it has been found necessary to take specialprecautions in the design and assembly of the components. The design ofthe tip 23 is shown in greater detail in FIG. 3. It has been foundadvantageous to form the tip 23 with an oversize head 37 and a stem 38.A bore 40 extends downwards through the stem 38 and to a point in thehead 37 adjacent the eventual position of the hemispherical end of thetip 23.

The plunger is assembled by inserting the stem 38 into the shaft 22 andloading the tip axially towards the shaft 22 with a load at which thetip material just starts to plastic flow. In one design of plunger wehave found 25 lb. to be a suitable load. A diametral drilling is madethrough the shaft 22 and stem 38 and a pin 39 is pressed therethrough.

The axial load is then removed from the tip 23 and it is rough turned toits hemispherical shape. The plunger is next annealed, conveniently ataround 60C. After cooling the tip 23 is formed to its finalhemispherical shape.

After the injector is completely assembled it is preferably raised to atemperature such as 130C at which the material of the tip 23 just beginsto plastic flow, to ensure good sealing of the tip 23 against theseating face 12.

If preferred suitable shapes other than hemispherical for the tip 23 andconical for the seating face 12 may be used. Furthermore other suitableways may be used for fastening the tip 23 to the shaft 22.

FIG. 2 shows in more detail one solenoid unit 32 according to thepresent invention. The solenoid unit has a cylindrical body 50 andintegral base 51, both of Swedish iron. A coaxial Swedish iron core 52is held in a bore in the base 51 by a ring of braze 53. The ring ofbraze also serves as a magnetic gap causing the lines of magnetic forcebetween the base and core 52 to pass out of the solenoid unit 32 andthrough the mushroomshaped head 29 which is thereby attracted upwarduntil it contacts the lower face of the solenoid unit 32. The terminals36 are connected to a wire winding 54. The upper part of the magneticcircuit is completed by Swedish iron lamina 55 which are a press fit onthe core 52 and inside the body 50 to ensure magnetic continuity. Thesolenoid unit 32 is sealed by a plastics capping 56. A ferromagnetic rod57 typically approximately 1/16 inch diameter is a sliding fit in anaxial bore 58 extending most of the way down the core 52. The rod 57 hasan enlarged threaded head 59 engaged in a threaded bore in the plasticscapping 56, the upper part of the core 52 or in both, whereby a fineadjustment may be made of the axial position of the rod 57 inside thecore 52.

In normal operation the fuel injector solenoid unit 32 is fed with astream of electrical pulses, during each of which the fuel is to beinjected into the engine. As the voltage of the leading edge of thepulse starts to rise the magnetic flux in the magnetic circuit starts torise correspondingly producing a rising force on the head 29 of theplunger and corresponding acceleration thereof.

The acceleration and motion of the plunger depends inter alia on thedifference between the simultaneous upwards magnetic force and downwardsforce due to the spring 26. The force pattern would therefore beexpected to depend on the value of the voltage of the relatively flattop of the electrical pulse, and variations in this peak voltage willproduce some variation in the time pattern of magnetic field and ensuingforce and plunger motion. This sensitivity of fuel flow to variations inthe pulse peak voltage can be reduced by arranging for at least a partof the magnetic circuit of the solenoid unit 32 and head 29 to becomemagnetically saturated at an electrical input voltage less than thepulse peak voltage. In this way the magnetic field, ensuing force andpattern of plunger movement will be significantly less sensitive topulse peak voltage.

Since several fuel injectors are commonly fed with the same electricalpulses on a multi-cylinder engine it is necessary for the injectors topass simultaneously equal quantities of fuel per pulse. We have foundthat a fine adjustment to the fuel flow versus pulse lengthcharacteristic of each injector can be made by altering the magneticfield in the magnetic circuit when saturation is reached. This is doneby axial movement of the rod 57, the core 52 being saturated by normalpulses. Due to the bore 58, the core 52, will become saturated at alower upwards force on the head 29 as the rod 57 is withdrawn.

I claim:

I. A method of making a fuel injector of the kind having a plungerincluding a metal portion which has a bore into which is fastened a stemof a tip of plastics or rubber-like material, said tip being for sealingagainst a seating face of the fuel injector, to close the fuel outletfrom said injector, said method including the steps of inserting thestem into the bore, loading the tip towards the metal portion with aload at which the tip material just starts to plastic flow, andmechanically securing the stem to the metal pertion while so loaded.

2. A method as claimed in claim 1 which includes drilling a diametralbore through the stem and metal portion and inserting a fastening pintherein while the tip is still loaded.

3. A method as claimed in claim 2, which includes just starts to plasticflow.

UNITED STATES PATENT OFFICE. CERTIFICATE OF CORRECTION 3,820 ,213 DatedJun 28 197 4 PETER MICHAEL KENT Patent No.

Inventor(s) It is certified that error appears in the above-identifiedpatent and that said Letters Patent are hereby corrected as shown below:

[30] Foreign Application Priority Data August 19, 1970 Great Britain"0012/70 Signed and sealed this 5th day of November 1974.

(SEAL) Attest:

McCOY M. GIBSON JR. C. MARSHALL DANN Arresting Officer Commissioner ofPatents USCOMM-DC 60376-P69 n u.s, eovzmmem rnm'nus OFFICE: Iano-sss-a:u.

F ORM P04 050 (10-69)

